Double crank controllable pitch propeller



Nov. 2, 1954 J, STRANDELL, ET AL 2,693,243

DOUBLE CRANK CONTROLLABLE PITCH PROPELLER 6 Shees-Sheet 1 Filed July 23, 1952 INVENTORS JOHN H. STRANDELL LEWIS A. RUPP ATTORNEY 5 1954 J. H. STRANYDELL ETAL 2,693,243

DOUBLE CRANK CONTROLLABLE PITCH PROPELLER Filed July 23, 1952 e Sheds-Sheet 2 INVENTORS JOHN H. .STRANDELL pews A. RUPP ATTORNEY s J. H. STRANDELL ETAL 2,693,243

DOUBLE CRANK CONTROLLABLB PITCH PROPELLER Filed Ju ly 23, 1952 e Sheets-Sheet 4 Nov. 2, 1954 RUPP BY ATTORNEYS 1954 J. H. STRANDELL ETAL 2,693,243

DOUBLE CRANK CONTROLLABLE PITCH PROPELLER 6 Sheets-Sheet 5 Filed July 23, 1952 INVENTORS JOHN :1. s1 osu.

LEWIS A. RU

ATTORNEYS Nov. 2, 1954 J. H. STRANDELL, ETAL 2,693,243

DOUBLE CRANK CONTROLLABLEI PITCH PROPELLER Filed July 23, 1952 6 Sheets-Sheet 6 INVENTORS JO H. STRA NDELL LE A. RUPP ATTORNEYS United States Patent DOUBLE CRANK CONTROLLABLE PITCH PROPELLER Application July 23, 1952, Serial No. 300,564

8 Claims. c1. 170-16032) (Granted under Title 35, S. Code (1952),,sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates to an improvement in controllable pitch propellers, such as used on ships, having blades which can be angularly adjusted in pitch from a remote point while the ship is waterborne. The blades are mounted on the propeller shaft hub and are simultaneously rotated about their own axis to achieve a change in pitch by a servo-motor mounted inside of the hub, which is responsive to a hydraulic power source located inside of the ship. The prior art discloses controllable pitch propellers of this general design but they are subject to many inherent disadvantages such as uneven and excessive wear on blade during surfaces, leaky hubs, improper hub lubrication, lack of positive means for movingthe blades to a forward pitch position in the event of a casualty to the blade moving means, etc. It 15 these deficiencies that have been corrected or eliminated by the present invention, culminating several years of research and testing of experimental models installed in operating shi s. r

I is therefore an object of the invention to provide an improved controllable pitch propeller suitable for use on marine vessels.

A further object of the invention .is the provision of a unique two-piston servo-motor for actuating the propeller blades.

Another object is the provision of a mechanism for changing the pitch of the blades which comprises a pair of crank arms connecting the servo-motor with the blades for accommodating large loads at high speeds and still maintaining a uniform bearing load on the structure.

A still further object of the invention is to provide a novel positive locking means for holding the propeller blades in a forward pitch position when the blade actuating means is inoperative.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description, when considered in connection with the accompanying drawings, in which like reference numerals designate like parts throughout the figures thereof and wherein:

Figure 1 is a sectional view in elevation longitudinally of the propeller hub, propeller shaft coupling and differential servo-motor.

' Figure 1A is a schematic showing of the controllable pitch propeller and control unit therefor as applied to a shi l igure 2 is a detailed sectional view taken on lines 2-2 of Figure 3 showing in elevation the servo-motor located in the propeller hub.

Figure 3 is a sectional view taken on -lines 3-3 of Figure 2.

Figure 4 is a detailed sectional view in elevation of the differential servo-motor shown .in the lower right side of Figure 1. y

Figure 5 is a detailedview taken on line 5-5 of Figure 1. 1

Figure 6 is adetailed sectional view taken on line 6-6 of Figure 1. I

Figure 7 is a detailed sectional view taken on line 7-7 of Figure 1.

Figure 8 is a plan view taken on lines 8-8 of Figure 1 showing the'crank clevis connectionsto the blade adapter.

Referring now to the drawings, wherein like reference characters designate like or corresponding parts throughout the several views, there is shown in Figure 1A, a propeller hub indicated at A, a thrust coupling connecting two sections of the propeller shaft at B and a differential servo-motor at C. Positioned between coupling B and differential servo-motor C is a bull gear which is appropriately shafted to the main propulsion equipment in the engineering spaces of the ship. The location 0 elements A, B and C relative to the ships structure is as follows: Differential servo-motor C is connected to the cover of a Kingsbury thrust bearing, the latter being secured to the forward end of the bull gear. Hollow propeller shaft 10 is shafted to the after end of the bull gear and extends for a short distance aft, where coupling B connects two sections of the propeller shaft together. Aft of this coupling, the propeller shaft 10 extends through the ships hull to hub A containing the propeller blades.

Referring now to hub A, shown in Figure 1, it will be seen that the shaft 10 fiaresoutwardly at 12 and is provided with screw threads 14 for receiving blade holding hub casting 16, and threadably secured to said hub casing 16 1s a spacer ring 18 :which properly positions and connects dunce cap 20 to the hub body. These members are snugly fitted to one another by means of packing so as to form a watertight fit, thus preventing the entry of Water into or the escape of oil from the hub, since the latter is adapted to be filled with oil at a pressure somewhat higher than the outside water pressure at all times. In some cases where the parts cannot form such a watertight fit, circular rubber seals are provided as shown at 22, for example, this particular seal being held in place by a circular ring 24 of like size and machine screws 26 which secure the seal and ring to the hub structure.

The blade holding spider 16 has four circular openings equidistantly spaced and extending around its periphery,

the diameter of each being sufficiently large to accommodate a propeller blade and its associated parts for securing the blade to hub casting 16. The forward end of the hub casting is provided with an extended portion 17 which is internally threaded and adapted to mate with the threads 14 on the flared portion of the propeller shaft The structural members of the hub casting for forming said circular openings are indicated at 19 (Figures l, 6 and 7) and provides the casting with the strength for supporting the blades. The propeller blades are respectively indicated at 28, 30, 32 and 34 and since each part employed for'holding the blades to the hub casting are exactly the same, description of only one of such blades and its associated parts will be given, with the same reference characters being used to denote l ke parts throughout the, corresponding views. Positioned deep in casting 16 is a bearing member 36 adapted to fit into a circular opening in said casting. This bearing member 36 has a flange 37 extending outwardly and at the top of the bearing for properly positioning saidbearmg 111 the casting opening. Rotatably mounted within said bearing is aicrank pin ring 38 formed in the shape of a cup, having a neck 40 extending downwardly from the bottom of the cup and is adapted to'fit in bearing 36, this crank pin serving the function of securing the blade to the propeller hub. The neck 40 is hollow and has a screw threaded opening 42 at its upper-end for receiving a crank pin ring puller when it is necessary to remove said crank pin ring from the bearing and hub casting for repairs. The outer upper peripheral portion of crank pin ring 38 is cut away forming a vertical wall 44 and horizontal seat 46 for reeciving bearing or bushing member 48. Bearings 48 are soft-soldered to ring 50 and are adapted to take the thrust exerted by blade 28 and is held in rigid position between casting 16 and crank pin ring 38 by means of ring 50 which is screw threaded to casting 16. It is to be understood that there are sixteen bearing surfaces for the four propeller blades, or four for each blade. They are the inner cylindrical bearings appearing at the point of contact of the outer peripheral portion of crank pin ring neck 40 with the inner surface of bearing member 36; the outer cylindrical bearing appearing at the point of contact of ring 38 with the inner portion of Patented Nov. 1 954 bearing members or bushings 48; the inner thrust bearing appearing at the point of contact of horizontal seat 46 (a) Propeller thrust and torque.

(b) The radial load. caused by the centrifugal couple ,du to the centrifugal force of the propeller blade itself when rotating.

(c) The forces from .the connecting rods turning the crank arms, consisting of the reaction forces, large. frictional forces and dynamic forces.

The inner thrust bearing takes the thrust caused by the centrifugal force of the propeller blade assembly. It also takes the force caused by the tipping action of the propeller .blade thrust and torque.

The outer thrust bearing takes the reaction force caused by tipping action of the propeller blade thrust and torque.

The inner portion of the cup shaped crank pin ring 38 is provided with female threads 52 which are of the type normally found in the breech mechanism of guns having a bore greater than, say, 3 inches, i. e. the threads are of the interrupted type in which the inner portion is threaded, and then every other 45 sector of threads is milled out leaving an inner cylindrical portion that alternately contains a sector of threads at 45 intervals, the remaining inner portion between each sector of threads being of a smooth surface and of the same curvature of said threads. The blade 28 has a reduced neck portion 54, having on its outer peripheral portion a like set of interrupted male threads 56 such as those explained above, which are adapted to mate with the threads on the crank pin ring. In operation, the male threads 56 of the blade neck are aligned with the smooth cut away section between the sectors of threads on the crank pin ring, the blade neck is dropped into the crank pin ring and when it bottoms, thev blade is turned 45 thus interlocking the threads and securing the blade in a fixed position. The blade and crank pin ring respectively have a slot 58 whichalign with one another when the blade is in a fixed or secure position and said .slots are'adapted to take a key 60, Figures 1 and 8, which positively locks the blade and crank pin ring in position. Cap 62 is screwed into the slotted blade portion so as to prevent the key from dropping out when the hubis rotated. The blade neck is hollowed out and contains a threaded opening 64 for receiving a blade. carrying tool when the blade is removed from the hub and transported from one location to another. In order toprevent leakage of water into-or loss of oil from the hub, circular rubber seal 66 is provided between metal ring 50 and blade 28.

As mentioned above, the hub A, with the attached blades 28, 30. 32 and 34 is rotated by the main propulsion equipment located inside the ship, and in order to eliminate stoppingand then physically reversing the direction of rotation of the propeller shaft to secure reverse movement of the ship, the angle of pitch of the propeller blades ,is changed, while the hub, and propeller shaft blades are rotating in the same direction, from an ahead to astern pitch, or vice versa, to effect such reversal in the direction of movementof the ship.

Each bladeis turned or rotated in its bearings by means of two crank clevices which are respectively connected to guides positioned on opposite sides of the center line of the blades, which in turn receive their power fromtwo pistons, one serving each of the guides. Referring more specifically to the drawings, it will be seen in Figures 1 and that crank pin ring'38 is recessed onopposite sides thereof to provide for free movement of crank clevises 80 and 82 which are respectively secured to the crank pin ring by means of pins 84 and 86. As shown in Figures 1 and 8 crank clevis 80 is connected at its other end to arm 92 of guide 88 by means of bolt 90. As more clearly shown in Figure 7, guide 88 comprises four guide arms, 92, 94, 96 and 98, each of said guide arms being respectively apertured to receive the securing means for each crank clevis, i. e. guide 88 has four arms which extendoutwa'rdly from its center and to each of these guide arms is secured a crank clevis and the other end of each crank arm, to which is also attached a crank clevis, extends to and is connected to its own crank pin ring. One such arrangement of guide arm, crankarm and crank pin ring is shown in Figure 1 and respectively designated by reference characters 92, 80 and 38. Formed integrally with guide 88 and extending on each side thereof is a hollow shaft 100, which extends forwardly toemergency piston 102 and aft to servo-piston 104.

Referring to Figures 1, 2 and 6, there is shown a servomotor mechanism at 106. This mechanism comprises a cylindrical housing 108 which is secured to hub casting 16 by meansof bolts 110, 112, 114 and 116 and serves as a Working area for guide piston 104 and second guidepiston 118. Movably mounted within said housing 108 and threadably connected with piston 118, is a second guide 120, which is slightly shorter but identical in construction to guide 88.. ,This second guide likewise has four arms, indicated by 122, 124, 126 and 128 in Figure 6,. each guide arm having an aperture therein through which is inserted a bolt 130, 132, 134 and 136 (one for each guide arm) for. securing to the guide arm, a crank clevis such as indicated at 138 and 140, each respectively being secured to guide arms 122 and 124. Each of the four crank. armsrespectively extend from each guide arm to one of the four crank pin rings, or in other words, eachiguide arm is connected to one of the four crank pin' rin'gs'. by means of a crank arm which transmits. the. power from the second guide piston to the crank pin ring for turning the blade.

, The servo-motor, mechanism specifically shown in Figure2. houses'thefrne'ans for making possible the movenient of guides 88 and .120 to eifect rotation of the propeller blades their sockets. This mechanism comprises a housing 108 which is secured tohub casting 16, as aforementioned, and pistons 104 and 118, shafted to their respective guides, are mounted for reciprocating movement withinv said housing. Guide shaft is hollow and slidably mounted therein is a hollow and movable valve stem 142 which is an extension of hollow control rod. 144 employed for supplying oil to the pistons. The. valve stem 142 is threadably secured to control rod 144 and contained thereon at 146 and 148 are the lands of the valve proper, which as shown, control the openings of ports 150, and 152 formed in guide shaft 100 and openings and 147 provide access from the hollow pressure oil to. the pistons 104 and 118 and returning same to the source of hydraulic supply. It, will be noted that there are several plugs inserted in shaft 100, such a s .indicated at 154, which merely serve to close the opening made, as a result of drilling holes in the inner partof said shaft, thatis, it is necessary to have openi'ngs extendingfrom the hollow portion of shaft 100 to the bored passageways and to provide such openings, it is convenient to drill such openings from outside the shaft, and when the dr illing proces's is completed, the outer openings are plugged since they are not necessary in the operation of the device. The after end of shaft 100 is closed by a plug .156 and similar plugs 158 are inserted in the bore R for containing the oil within said shaft. As clearly shown in Figure 2, the pistons carry oil seal rings 16,0 and the pistons are secured to the guide shafts 100- and 120 by ring's 162 and 164' respectively, each of said rings having grooved openings 166 to facilitate removal of said rings from the guide shafts. In order to prevent each of the guide shafts from turning relative to one another, a key.1 68 is embedded in the outer portion of guide. shaft100 and. the shaft for guide 120 is appropriately slotted at 170 to the same size as the key so thatthe key rides inthe slot, thus preventing relative rotary movement of one shaft with respect to the other.

' sponds to an ahead pitch on the blades.

of the invention, oil under pressure from differential servomotor unit C flows through control rod 144 and valve stem 142, through openings 145 and 147 to the space enclosed by valve lands 146 and 148. When it is desired to change thepitch of the blades to an ahead pitch position, the control rod 144 is caused to be moved in an aft or rearward direction which causes valves 146 and 148 to uncover ports 150 and 152. Oil then flows through ports 150 into the space between pistons 104 and 118 where the oil pressure is exerted against exposed piston surfaces to move said pistons away from each other. Since piston 104 is directly connected to each propeller blade through guide shaft 100 and guide arms 92, 94, 96 and 98 with a crank arm extending from each of said guide arms to the crank pin ring for each blade, it is evident that the blade will be turned in a counterclockwise direction which corre- Piston 118 moves in the opposite direction from piston 104 and is likewise directly connected to each of the blades by means of a guide shaft and guide arms 122, 124, 126 and 128 and connected between each of the guide arms and the crank pin ring for each blade are crank arms, two of same being indicated by- 138 and 140. It is to be understood that two crank arms are connected to each crank arm ring, one arm extending between guide 88 and one side of the crank pin ring and the other arm extending between guide 120 and the other or opposite side of the crank pin ring, as clearly shown in Figure 8. Movement of piston 118 therefore aids in turning the blades to the ahead pitch position. The-oil displaced by such outward movement of piston 118 causes the oil to flow from area Y through passageway 172 to area X where it joins with the oil therein to return to the source through passageway SR, ports 152, past valve 146 which partially uncovers ports 152, into passageway R and back to the oil supply pump 268 in unit C. When the control rod 144 and attached valve stem 142 is initially moved and stopped, it remains in the stopped position until moved again. The piston 104, along with ported shaft 100, serves as a follow-up since the oil pressure will move the piston until the ports in shaft 100 align with valves 146 and 148 and when such alignment occurs, oil flow to the piston is stopped and stoppage of piston movement subsequently follows. The pistons will not be moved until the control rod is actuated to uncover the ports and to commence repetition of the process.

When it is desired to reverse the pitch of the propeller to achieve astern movement of the ship, the control rod 144 is moved in the opposite direction, i. e. forwardly. This movement causes valve 148 to uncover ports 150 and valve 146 uncovers ports 152. Oil flows through valve stem passage S, through openings 145 and 147, ports 152 to passageway S-R, and into area X where this oil pressure is exerted against the outer face of piston 104; passageway 172 which connects with area X, transmits the oil pressure to area Y where it acts against the outer face of piston 118, the oil pressure causing both of said pistons to move inwardlyor toward one another. The oil displaced by such inward movement flows from between said pistons, through ports 150, ports 174 to return passageway R which carries the oil back to the source in unit C. This direction of piston movement causes the blades to be rotated in a clockwise direction which corresponds to reverse pitch for astern movement of the ship. The structure connected between the pistons and the propeller blade is of course the same as that described above in relation to movement of the blades to an ahead pitch position. It is to be noted that passageway SR in one case acts as a supply conduit and in the other, serves as a return conduit for the oil.

Referring now to unit B, shown in Figure 1, there is shown the means for moving the blades to the ahead or forward pitch position in the event of a casualty in the hub mechanism so that the ship can be moved, even though the ships main hydraulic system becomes inoperative. The structure comprises two hollow tubes which extend rearwardly between the control rod 144 and propeller shaft to a stationary plate 180 which is snugly fitted by means of packing within the propeller shaft to prevent leakage of oil from the hub A into the forward section of said shaft. -The purpose of upper supply line 176 is toprovide means for supplying oil to the space between plate 180 and piston 102 when it is necessary to manually change the position of the blades, while conduit 178 serves as an air vent to vent air from said space to the atmosphere. The means for closing both conduits comprises two plugs 182 and 184 respectively, which normally, are open to the atmosphere. In operation, in the case of an emergency when it is necessary to set the pitch of the blades to a forward position, the propeller shaft is stopped, hand pump 186 with its associated oil supply tank 188 is connected by conduits to plug 182 and oil manually pumped into the area between piston 102 and plate which displaces air therebetween. The air fiows out through conduit 17 8 to plug 184 and when oil commences to flow out of plug 184 the latter is closed, as by means of a cock, or the plug completely removed and replaced by a solid plug. The continued operation of the pump builds up hydraulic pressure behind piston 102, until it is suflicient to move the blades to an ahead position. The cock on plug 182 is then moved to a closed position and the pump disconnected therefrom so that free rotary movement of the propeller shaft may be obtained.

A coupling is shown in Figure l and comprises one of several of this type that are employed for connecting various sections of the propeller shaft. The coupling comprises a cylindrical section 190 which is splined to shaft 10 and grooved at 192 to take half-moon shaped keys 194. The forward section of the propeller shaft, alsoindicated as 10, is outwardly flared at 196 and apertured to take bolts 198 which extend through and secure said flare, key 194 and section 190 together so as to form a shaft rigid in construction.

Referring now to the differential servo-motor mechanism indicated by C in Figures 1 and 4, there is shown a stationary thrust plate 200 comprising a part of a Kingsbury thrust bearing used for taking the thrust developed by the propeller blades. Plate 200 is centrally apertured to enclose a short cylindrical shaft 202 which is connected to propeller shaft 10 by means of bolts 204. Control rod 144 is keyed to shaft 202 in order to secure rotary movement of said control rod. Secured between shaft 202 and thrust bearing plate 200 is a seal 206, held in place by appropriate means for preventing leakage of oil from the return line R to the thrust bearing. The following description of the differential servo-motor unit C is the same as that disclosed in the application of John H. Strandell, Serial No. 296,515, filed June 30, 1952. Secured to the forward end of thrust bearing plate 200 by means of bolts 208 is a first housing 210 which completes return passage R and fixed in sealed relation to said first housing 210 by bolts 212, is a second housing 214 for containing control rod extension 216, said second housing forming with said first housing an oil chamber 218 adapted to receive oil at pressures approximately 1500 p. s. i. which is supplied to pistons 104 and 118 through control rod 144. Mounted above, the second housing is a control box 220 containing the means for controlling the supply of oil to said chamber 218. Referring more specifically to these parts, first housing 210 is centrally apertured for receiving the forward end of control rod 144, and positioned around said rod in fluid tight relation therewith and with the first housing is a high pressure packing gland 222 secured to the first housing by the usual appropriate means including a nut 224 for taking upon the packing when it becomes worn. In the specific embodiment shown, is under a pressure of approximately 15 p. s. i. while oil chamber 218 contains pressures in the neighborhood of 1500 p. s. i., although other pressures may be used in this system, and the packing 222 serves to prevent leakage of oil from one chamber to the other. ing 210 ing said oilto sump 266 for further use. ward end of control rod 218, which is supplied with oil by conduit 282, and has three openings in the outer end thereof, one of such openings being indicated at 228, for supplying oil through the control rod to pistons 104 and 118 for changing the pitch of the propeller blades.v Forwardly of these openings, the control rod is sequentially reduced in diameter to form a first reduced portion 230 and a second reduced portion 232. Mounted on the second reduced portion 232 are two ball bearing races 234 comprising inner and outer bearing shells 236 and 238 respectively, with ball bearings 240 secured therebetween. The ball bearing races 234 are held in place by a nut 242 which presses the races into engagement with the flat forward.

surface of first reduced portion 230, and the after end the oil return passageway R- of control rod extension 216 is hollowed out to form an opening for nut 242 and said extension threaded on its outer exterior end. Threadably secured to said extension is a dilferential servo-motor piston 244 provided with oil seal rings 246 on its outer periphery and having a lip or flange 248 which aids in holding the bearing races in position. Nut 250, which forms the other end of piston 244, serves to position control rod extension 216 in housing 214, and locks the piston 244 to said extension. The hollow central portion of second housing 214 forms with the control rod extension 216, an oil chamber 252, which is closed at its outer or forwardend by a plug 254 secured to housing 214 by bolts 257 or other similar securing means, such as screw threads or a force fit. The plug 254 is equipped with oil seal rings at 256 and 258. for preventing leakage of the high pressure oil from chamber 252. The control rod extension reciprocates within the plug opening and attached to the forward end thereof is an indicating rod 260,.which mechanically indicates the exact pitch to which the blades are set.

There are therefore, three oil containing chambers located in the differenial servo-motor section of this invention, namely, chambers R, 218 and 252, chamber R being the low pressure return from the hub to sump 266 and pump 268 while chamber 218 serves to supply oil to the hub pistons by way of the control rod and to exert a force on dilferential servo-motor piston 244 for moving the control rod in a forward direction, and chamber 252 serves to house the oil for exerting a moving force against nut 250, which in eflect acts asa piston, for moving the control rod in an after or rearward direction. I There is also shown schematicallyfor the purposes. of illustration a three-way pilot valve. 270 having a chamber port 272 connected to the chamber 252 by conduit 264. An inlet port 273 is connected to the oil line 282 through the chamber 218 and conduit 262, and an exhaust port 274 which is connected by conduit 278 to the, oil sump 266 through the. oilv flowregulator valve 280. A piston 276 in the pilot valve 270 serves to seal the chamber port 272, interconnect the chamber port 272 and inlet port 273, or to interconnect the. Chamber port 272 and theexhaustport 274, as hereinafter ex,- plained. The means for controlling operation of pilot valve 270 is nota part of this invention but it maybe noted that the pilot valve is. controlled by electrical se'lsyns operated from the bridge of the ship.

, The oil pressure in chamber218 is substantially constant, and therefore exerts a susbtantially constant forward thrust on the servo-motor piston 244, However, the servo-motor piston 244 exposes an area to oilchamber 252 which is substantiallylarger than itsiarea exposed to oil chamber 218, whereby a lower pressure in oil chamber 252 will overcome the higher pressure in oil chamber 218 to produce an aft movement of the servo-motor piston244. W H

In operation, with the, pilotvalve piston 276 blocking ports 272 and 274, oil at a constant pressure of 1500 p. s. i. is supplied by pump 268 to oil chamber 218 which furnishes the oil to and through control rod l44 to the pistons located in hub A. This oil is further supplied through conduit 262 to pilot valve 270, conduit264 and oil chamber 252 being filled with oil. When it is desired to change the pitch of the propeller blades to, say, an ahead or forward pitch position, the pilot valve piston is operated, moving it to an ahead position, which position interconnects the, chamber port 272 and the inlet port 273. Oil now flows from chamber 218 to chamber 252, thus increasing the, pressure in chamber 252 to move the control rod 144 in an astern direction. Astern movement of the control rod uncovers ports 15%! in hub A, causing oil to flow between pistons 104 and 118 for moving the blades to an ahead or forward pitch position. When the blades have reached the desired position (as remotely indicated on the bridge of the ship), pilot valve piston 276 is then moved to recover port 272, thus blocking off the flow of oil to or from chamber 252. A substantial reversal of this, process occurs when the propeller blades are changed to a reverse pitch position, since the pilot valve 276 is. then moved in a rearward movement to interconnect the chamber port 273 and exhaust port 274. Oilpressure in chamber 218 then forces oil from chamber 252 to the sump 266, and moves the controlrod 144 in a forwarddir'ection. This rod action uncovers ports 152 allowing oil. to flow to opposite sides of pistons 1Q4 and 11.8 whiclrmoves the blades to a reverse pitch position, and when the desired blade angle is reached, the pilot valve piston is then caused to recover port 272 and the remaining oil in chamber 252 is trapped therein.

It should be understood that the foregoing disclosures relate. to only a preferred embodiment of the invention and that numerous modifications or alterations may be made therein without departing from the spirit and the scope of the invention as set forth in the appended claims.

What is claimed is:

1. In combination, a controllable pitch propeller having blades and a hub, means for changing the pitch of said blades, said means comprising a pair of pistons in said hub, a guide connected to each of said pistons, a plurality of crank arms, means connecting said crank arms at one end to said guides and at the other end to said blades, a source of fluid supply, control means interconnecting said source of fluid supply with said pistons for regulating supply of fluid to said pistons, fluid pressure responsive means controlling said control means, said fluid responsive means comprising a housing, an actuating piston within said housing, means connecting said actuating piston with said control means, conduit means connecting said source of fluid supply with said actuating piston for exerting a constant fluid pressure against opposite sides of said actuating piston, and means in said conduit means for varying the fluid pressure acting against one side of said actuating piston so as to move said control means to provide fluid pressure to said pistons in said hub.

2. In combination, a controllable pitch propeller having blades and a hub, means for changing the pitch of said blades, said means comprising a pair of pistons in said hub, a common cylinder for said pistons attached to said hub, means connecting said pistons to said blades, a control rod, means movably mounting said control rod within a hollow shaft extending from one of said pistons to and through the central portion of the other of said pistons, passageway means in said cylinder interconnecting opposite ends of said pistons, valve ports in said shaft, valve lands mounted on said control rod for engaging said valve ports, a source of fluid supply, means connecting said source of fluid supply with said valve ports and thereby with said cylinder, fluid pressure responsive means for controlling the movements of said control rod, said fluid pressure responsive means comprising a housing, an actuating piston within said housing, means connecting said actuating piston with said control rod, conduit means interconnecting said source of fluid supply with said actuating piston, and pilot valve means in said conduit means for moving said actuating piston so that the movement of said actuating piston is imparted to said control rod for controlling the flow of fluid to said pistons.

3. In combination, a controllable pitch propeller having blades and a hub, means for changing the pitch of said blades, said means comprising a pair of pistons in said hub, a cylinder having closed ends attached to said hub for housing said pistons, means connecting said pistons with said blades, a source of fluid supply, control means in said cylinder for connecting said source of fluid supply with said pistons, a control rod connected at one end to said control means, fluid pressure responsive means adjacent said hub for controlling said control means, said fluid pressure responsive means comprising a first housing for supporting said control rod, a second housing, means forming a longitudinally hollow bore in said second housing, means securing said first housing to said second housing and forming therewith a fluid chamber, an actuating piston secured to the other end of said control rod extending through said fluid chamber and into said bore of said second housing, means connecting said source of fluid supply to said fluid chamher, a pilot valve, a first conduit connecting said pilot valve with said bore of said second housing, a fluid sump, a third conduit connecting said sump with said pilot valve, a pilot valve piston, and means adapted to move said pilot valve piston for controlling the flow of fluid through said conduits to said actuating piston.

4. In a controllable pitch propeller having blades and a hub, a hollow propeller shaft secured to said hub, means for changing the pitch of said blades, said means com prising a servo-motor mechanism in said hub, means connectingsaid mechanism with said blades, a hollow shaft secured to a forward end of said servo-motor mechani'sm and extending into the after section of said propeIler shaft, emergency means for changing the pitch of 9 said blades, said emergency means comprising a stationary plate encircling said hollow shaft and rigidly mounted in said hollow propeller shaft, a cylindrical ring forming a piston secured to said hollow shaft; said hollow shaft, piston, plate and propeller shaft forming a fluid receiving chamber, a pair of conduits, a source of emergency fluid supply, said conduits respectively connecting said chamber with said source of emergency fluid supply and with the atmosphere and means for selectively closing said conduits so that the application of fluid pressure to said piston moves said servo-motor to 1elffgct a change in pitch in the blades mounted on said 5. In a controllable pitch propeller having blades and a hub, means for changing the pitch of said blades, said means comprising a hub casting in said hub, a centrally hollow bore in said hub casting, a plurality of propeller blades radially extending from and secured to said hub casting, a servo-motor mechanism, said mechanism comprising a cylindrical housing attached to said hub, a first piston within said housing, a first hollow and longitudinally bored shaft movably mounted within said bore of said hub casting and secured at its one end to said first piston and adapted to extend into a propeller shaft at its other end, a first guide member having a plurality of arms and formed as an integral part of said first shaft, a plurality of crank arms, means connecting said crank arms at one end to said guide arms and at the other end to said blades, a second piston within said housing, a second shaft secured at its one end to said second piston and terminating at its other end in a second guide having a plurality of arms, means mounting said second piston and said second shaft in surrounding relation with said first shaft and adapted to reciprocate therealong, a plurality of second crank arms, means connecting said second crank arms at one end to said second guide arms and at the other end to said blades so that opposite movements of said pistons produce a cumulative turning torque on said blades, a hollow control rod having valve lands thereon, means mounting said control rod longitudinally Within said first hollow shaft and adapted to be connected to an actuating piston remotely located from said hub, valve ports positioned in said first hollow shaft between said pistons and controlled by said control rod and means adapted to supply a fluid through said control rod and said ports to move said pistons in opposite directions.

6. In a controllable pitch propeller having blades and a hub, a hollow propeller shaft attached to said hub, means for changing the pitch of said blades, said means comprising a hub casting in said hub, a plurality of propeller blades secured to said hub casting, a servomotor mechanism, said mechanism comprising a closed housing attached to said hub, a first piston in said housing having a first hollow shaft passing centrally through said hub casting and terminating in said propeller shaft, a second piston in said housing having a second hollow shaft mounted for reciprocating movement on said first hollow shaft, a pair of guides respectively secured to said hollow shafts, a plurality of crank arms, means connecting said crank arms at one end to said guides and at the other end to said blades, a hollow control rod reciprocatingly mounted within said first hollow shaft, a source of fluid supply connected to said hollow control rod, and means controlling said supply of fluid from said control rod to said pistons.

7. The combination according to claim 6 wherein each of said propeller blades is secured to said hub casting through means of a crank pin ring, said crank pin ring comprising a hollow cup-shaped member having a neck extending downwardly therefrom, means rigidly aifixing said blade in said crank pin ring, said rigidly afiixing means comprising a set of interrupted female threads on the inner portion of said crank pin ring, a set of interrupted male threads on the outer neck portion of said blade, a slot formed in each of said crank pin rings and said blades which are adapted to be aligned with one another, a key for said aligned slots, whereby said blades are inserted in said crank pin ring and rotated less than into a fixed position prior to the insertion of said key in said slot.

8. The combination according to claim 6 wherein emergency means are provided for changing the pitch of said blades, said emergency means comprising an emergency piston attached to said first hollow shaft and positioned within said propeller shaft, stationary means in said propeller shaft forming a closed chamber with said emergency piston, and fluid pressure supply means connected with said chamber for moving said emergency piston in a rearward direction for changing the pitch of said blades.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,723,617 Hele-Shaw et al. Aug. 6, 1929 2,355,039 Eves Aug. 1, 1944 2,456,361 Atteslander Dec. 14, 1948 2,513,546 Atteslander July 4, 1950 2,513,660 Martin et al. July 4, 1950 2,518,925 Nussbaum Aug. 15, 1950 FOREIGN PATENTS Number Country Date 301,635 Germany Apr. 7, 1920 493,416 Great Britain Oct. 7, 1938 

